Levels of whole-body vibration affecting human vision.

A visual task was devised to determine the minimum levels of whole-body vibration that affect human vision. This task was the perception of the blur-due to eye motion-of an image of a stationary point source of light and is considered to be as sensitive as any alternative measure of the effects of vibration on visual acuity. Minimum levels of sinusoidal vertical vibration required to produce blur have been determined in a group of 12 subjects seated in a posture that maximised the sensation of vibration at their heads. The effect of vibration frequency (from 7 to 75 Hz) differed between subjects and there was a large individual variability in the levels of both head and seat vibration required to produce blur at any frequency. This intersubject variability has been compared with the potentially large intrasubject variability due to changes in body posture. The experimental results have led to the tentative recommendation of vibration levels below which vibration is not normally expected to reduce visual acuity.